The present invention relates to pneumatically actuated devices and more particularly to a crust-breaking device for use in processing molten material.
Pneumatic control valves or control valve systems are commonly used in various operations or processes for controlling the flow of pressurized control air to and from a pneumatically-operated cylinder or other such actuating device having a movable work-performing member or armature. Frequently, however, the pneumatically-operated device is not constantly in motion, with the work-performing member being held in a stationary position during various portions of the operation. The maintaining of full line control air pressure during periods when the movable armature of the pneumatically-operated device is required to be held in a stationary position has been found to be wasteful of energy required to run compressors or other such devices.
In many pneumatically-operated systems, especially in systems employing older equipment, leakage inevitably occurs in the pneumatically-operated device or in related systems or subsystems. The maintaining of full line control air pressure and flow in order to compensate for such leakage has also been found to be expensive and wasteful in terms of energy usage, especially in systems such as those described above where a movable armature is required to be held in a stationary position during various portions of the operation of the system.
Such pneumatically-operated devices are commonly employed in systems that process molten metal. Typical processing systems include a large receptacle for retaining a mass of molten metal therein. A surface of the mass is generally exposed to atmosphere and thus exothermic heat transfer occurs from the mass, thereby cooling the top surface of the mass and forming a crust. The crust formation is detrimental to the material processing and pneumatically-operated devices, such as that described herein, are commonly employed for intermittently breaking the crust. However, it has been recognized in the industry that contact between the pneumatically-operated devices and the mass results in heat transfer from the mass to the pneumatically-operated devices. This has been found to be detrimental to energy efficiency in the processing of molten metals because the addition of heat is required to compensate for that lost through the heat transfer.
Thus, the need has arisen for a pneumatic control valve or control valve system that is capable of addressing the above-mentioned problems in a more energy-efficient manner. To this end, in accordance with the present invention, it has been found that a pneumatically-operated cylinder or other such device can be held in a stationary or static condition with minimal air pressure. In addition, it has been found that it is not necessary to continuously compensate for leakage in the pneumatically-operated system or device, especially during the above-mentioned static modes of operation. Instead, a brief, instantaneous compensation of air pressure may be used to maintain the pneumatically operated system or device in the static modes of operation. Further, and in accordance with the present invention, the effects of heat transfer may be significantly reduced by limiting the time the pneumatically-operated device and the mass remain in contact with one another during a crust breaking process.
Accordingly, the present invention provides a control system for selectively controlling movement of a device between first and second working positions. The control system comprises a control actuator selectively actuated to enable fluid communication between the control system and a source of pressurized fluid, a driving system for selectively driving the device between the first and second working positions in response to the control actuator enabling fluid communication between the control system and the source of pressurized fluid, a sensing system for identifying either of the first and second working positions of the device and manipulating a flow of pressurized fluid to the device in response thereto, and a monitoring actuator selectively actuated by the sensing system for relieving the flow of pressurized fluid to the driving system, wherein the monitoring actuator remains actuated until the control actuator is deactuated.
The present invention further provides a system for processing molten material. The system includes a retainer for retaining a mass of molten metal wherein said mass of molten metal periodically forms a crust on a top surface, a device operable between first and second working positions for selectively breaking the crust, and a control system for controlling operation of the device between the first and second working positions. The control system includes a control actuator selectively actuated to enable fluid communication between the device and a source of pressurized fluid, a driving system for selectively driving the device between the first and second working positions in response to the control actuator enabling fluid communication between the device and the source of pressurized fluid, a sensing system for identifying either of the first and second working positions of the device and manipulating a flow of pressurized fluid to the device in response thereto, and a monitoring actuator selectively actuated by the sensing system for relieving the flow of pressurized fluid to the driving system, wherein the monitoring actuator remains actuated until the control actuator is deactuated.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.